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Dense La 0.8 Sr 0.2 MnO 3 ͑LSM͒ electrodes were patterned by photolithography and fabricated via pulsed-laser deposition on Y 2 O 3-stabalized ZrO 2 ͑YSZ͒ electrolytes. Impedance analysis shows that the interfacial polarization resistance decreases significantly as electrode thickness drops below a critical value, beyond which the top surface of the LSM becomes active for oxygen reduction. However, when the LSM electrodes become too thin, the in-plane sheet resistance of the LSM starts to limit the utilization of the electrodes along their length. Quantification of the characteristic thickness is important not only to intelligent design of practical mixed-conducting electrodes but also to electrode design for fundamental studies.

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Grain boundary structure-property relationships influence bulk performance and, therefore, are an important criterion in materials design. Materials scientists can generate different grain boundary structures by changes in temperature, pressure, and chemical potential because interfaces attain their own equilibrium states, known as complexions. Complexions undergo first-order transitions by changes in thermodynamic variables, which results in discontinuous changes in properties.Grain boundary complexion engineering is introduced in this paper as a method for controlling complexion transitions to improve material performance. This International Conference on Sintering 2017 lecture describes the tools for grain boundary complexion engineering: complexion equilibrium and time-temperaturetransformation (TTT) diagrams. These tools can be implemented in processing design to tailor grain boundary properties, including grain boundary mobility.While impactful, these diagrams are often limited in scope because they are currently empirically derived. This article discusses how measurement techniques can be combined with data analytical methods to build mechanistically derived complexion equilibrium and TTT diagrams.

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To determine how grain-boundary composition affects the liquid phase sintering of MgO-free Bayer process aluminas, samples were singly or co-doped with up to 1029 ppm Na 2 O and 603 ppm SiO 2 and heated at 1525°C up to 8 h. Na 2 O retards densification of samples from the onset of sintering and up to hold times of 30 min at 1525°C compared to the undoped samples, but similar to the as-received, MgO-free Al 2 O 3 , Na 2 Odoped samples sinter to 98% density with average grain sizes of~3 lm after 8 h. Increasing SiO 2 concentration significantly retards densification at all hold times up to 8 h. The estimated viscosities (20 -400 PaÁs) of the 0.3 to 1.8 nm thick siliceous grain-boundary films in this study indicate that diffusion greatly depends on the composition of the liquid grain-boundary phase. For low Na 2 O/SiO 2 ratios, densification of Bayer Al 2 O 3 at 1525°C is controlled by diffusion of Al 3+ through the grain-boundary liquid, whereas for high Na 2 O/SiO 2 ratios, densification can be governed by either the interface reaction (i.e., dissolution) of Al 2 O 3 or diffusion of Al 3+ . Increasing Na 2 O in SiO 2 -doped samples increases diffusion of Al 3+ and Al 2 O 3 solubility in the liquid, and thus densification increases by 1%. Based on these findings, we conclude that Bayer Al 2 O 3 densification can be manipulated by adjusting the Na 2 O to SiO 2 ratio.